protocols/is: Implement first parts of IS API

lib/matrix_sdk/protocols/is.rb

 module MatrixSdk::Protocols::IS
-  raise 'Not implemented yet'
+  def identity_status
+    request(:get, :identity_api_v1, '/')
+  end
+
+  def identity_get_pubkey(id)
+    id = CGI.escape id.to_s
+
+    request(:get, :identity_api_v1, "/pubkey/#{id}")
+  end
+
+  def identity_pubkey_isvalid(key, ephemeral: false)
+    if ephemeral
+      request(:get, :identity_api_v1, '/pubkey/ephemeral/isvalid', query: { public_key: key })
+    else
+      request(:get, :identity_api_v1, '/pubkey/isvalid', query: { public_key: key })
+    end
+  end
+
+  def identity_pubkey_ephemeral_isvalid(key)
+    identity_pubkey_isvalid(key, ephemeral: true)
+  end
+
+  def identity_lookup(medium:, address:)
+    request(:get, :identity_api_v1, '/lookup', query: { medium: medium, address: address })
+  end
+
+  def identity_bulk_lookup(threepids)
+    request(:post, :identity_api_v1, '/bulk_lookup', body: { threepids: threepids })
+  end
+
+  # XXX
 end